Radiation-sensitive materials, including light-sensitive materials, such as photographic materials, may utilize filter dyes for a variety of purposes. Filter dyes may be used to adjust the speed of a radiation-sensitive layer; they may be used as absorber dyes to increase image sharpness of a radiation-sensitive layer; they may be used as antihalation dyes to reduce halation; they may be used to reduce the amount or intensity of radiation from reaching one or more radiation-sensitive layers, and they may also be used to prevent radiation of a specific wavelength or range of wavelengths from reaching one or more of the radiation-sensitive layers in a radiation-sensitive element. For each of these uses, the filter dye(s) may be located in any number of layers of a radiation-sensitive element, depending on the specific requirements of the element and the dye, and on the manner in which the element is to be exposed. The amount of filter dyes used varies widely, but they are preferably present in amounts sufficient to alter in some way the response of the element to radiation. Filter dyes may be located in a layer above a radiation-sensitive layer, in a radiation-sensitive layer, in a layer below a radiation-sensitive layer, or in a layer on the opposite side of the support from a radiation-sensitive layer.
Photographic materials often contain layers sensitized to different regions of the spectrum, such as red, blue, green, ultraviolet, infrared, X-ray, to name a few. A typical color photographic element contains a layer sensitized to each of the three primary regions of the visible spectrum, i.e., blue, green, and red. Silver halide used in these materials has an intrinsic sensitivity to blue light. Increased sensitivity to blue light, along with sensitivity to green light or red light, is imparted through the use of various sensitizing dyes adsorbed to the silver halide grains. Sensitized silver halide retains its intrinsic sensitivity to blue light.
There are numerous applications for which filtration or absorbance of very specific regions of light are highly desirable. Some of these applications, such as yellow filter dyes and magenta trimmer dyes, require non-diffusing dyes which may be coated in a layer-specific manner to prevent specific wavelengths of light from reaching specific layers of the film during exposure. These dyes must have sharp-cutting edges on the bathochromic (long-wavelength) side of the absorbance envelope to prevent light punch through without adversely affecting the speed of the underlying eraulsions. In other applications, it is desirable to allow passage of light below a certain wavelength. In these cases it is desirable to have a dye which is very sharp-cutting on the hypsochromic (short-wavelength) edge of the absorbance envelope. Depending on the location of these filter layers relative to the sensitized silver halide emulsion layers, it would also be desirable to have non-diffusing, layer-specific filter dyes with absorption spectra which are sharp-cutting on the hypsochromic edge as well as the bathochromic edge. Such dyes are sometimes known as "finger filters". Preferably these dyes should exhibit high extinction coefficients, narrow half bandwidths and sharp cutting hypsochromic and bathochromic absorption envelopes when incorporated into imaging elements including photographic elements. Typically, to achieve these properties, isotropic solutions of dyes have been incorporated. Dyes introduced by this method, however, often wander into adjacent layers causing problems such as speed loss or stain, and cannot be coated in a layer-specific manner without the use of mordants. Solubilized dyes may be mordanted to prevent wandering through adjacent layers. While the use of polymeric mordants can prevent dye wandering, such mordants aggravate the stain problem encountered when the dye remains in the element through processing.
Dyes with a high extinction coefficient allow maximum light absorption using a minimum amount of dye. Lower requisite dye laydown reduces the cost of light filtration and produces fewer processing by-products. Lower dye laydowns may also result in reduced dye stain in short duration processes.
Finger filters such as described above are highly desirable for other uses such as protecting silver halide sensitized emulsions from exposure by safelights. Such dyes must have absorbance spectra with high extinction coefficients and narrow half bandwidths, and sharp cutting absorbance envelopes to efficiently absorb light in the narrow safelight-emitting region without adversely affecting the speed of the sensitized silver halide emulsions. This affords protection for the sensitized emulsion from exposure by light in the safelight's spectral region. Useful absorbance maxima for safelight dyes include, but are not restricted to 490-510 nm and 590-610 nm.
Similar properties are required for infrared absorbing filter dyes. Laser-exposed radiation-sensitive elements require high efficiency light absorbance at the wavelength of laser emission. Unwanted absorbance from broadly absorbing dyes reduces the efficiency of light capture at the laser emission wavelength, and requires the use of larger amounts of dye to adequately cover the desired spectral region. In photographic elements, unwanted absorbance may also cause speed losses in adjacent silver halide sensitized layers if the photographic element has multiple sensitized layers present. Useful finger filter absorbance maxima for absorbing laser and phosphor emissions include but are not restricted to 950 nm, 880 nm, 830 nm, 790 nm, 633 nm, 670 nm, 545 nm and 488 nm.
In some radiation sensitive elements, including dry process imaging films, it is necessary to provide light filtration or antihalation at deep cyan and infrared wavelengths. Typically such protection has been achieved using water or solvent soluble dyes or milled solid particle dyes. Typically, water-soluble dyes forming isotropic solutions can provide relatively sharp, high extinction absorbance, but are prone to interlayer wandering.
One common use for filter dyes is in silver halide light sensitive photographic elements. If, prior to processing, blue light reaches a layer containing silver halide which has been sensitized to a region of the spectrum other than blue, the silver halide grains exposed to the blue light, by virtue of their intrinsic sensitivity to blue light, would be rendered developable. This would result in a false rendition of the image information being recorded in the photographic element. It is therefore a common practice to include in the photographic element a material that filters blue light. This blue-absorbing material can be located anywhere in the element where it is desirable to filter blue light. In a color photographic element that has layers sensitized to each of the primary colors, it is common to have the blue-sensitized layer closest to the exposure source and to interpose a blue-absorbing, or yellow filter layer between the blue-sensitized layer and the green- and red-sensitized layers.
Another common use for filter dyes is to filter or trim portions of the UV, visible or infrared spectral regions to prevent unwanted wavelengths of light from reaching sensitized emulsions. Just as yellow filter dyes prevent false color rendition from the exposure of emulsions sensitized to a region of the spectrum other than blue, filter dyes absorbing in the UV, magenta, cyan and infrared spectral regions can prevent false color rendition by shielding sensitized emulsion layers from exposure to specific wavelength regions. One application of this strategy is the use of green-absorbing magenta trimmer dyes. In one type of typical color photographic element containing a layer sensitized to each of the three primary regions of the visible spectrum, i.e., blue, green, and red, the green-sensitized layer is coated above the red-sensitized layer and below the blue-sensitized layer. Depending on the chosen spectral sensitivity maxima for the sensitized silver halide layers, there may be a region of overlap between the spectral sensitivities of the green and red emulsions. Under such circumstances, green light which is not absorbed by the green-sensitive emulsion can punch through to the red sensitive emulsion and be absorbed by the leading edge of the red spectral sensitizing dye. This crosstalk between the green and red emulsions results in false color rendition. It would, therefore, be highly desirable to find a green-absorbing filter dye which upon incorporation into a photographic element would absorb strongly around I-he spectral maximum of the green-sensitized emulsion, and possess a sharp cutting bathochromic absorbance such that there is no appreciable absorbance just bathochromic to its absorbance maximum. A sharp-cutting bathochromic edge on a filter or trimmer dye enables excellent color reproduction with minimum speed loss by absorbing light efficiently up to its absorbance maximum, but very little if any just past its absorbance maximum. For example, a magenta trimmer dye (green absorber) which is only moderately sharp-cutting on the bathochromic edge may function adequately as a filter dye, but its unwanted absorbance in the red region past its .lambda..sub.max will rob the red-sensitive emulsion coated below it of red light and hence speed. Though the position of optimal absorption maximum for a magenta trimmer dye will vary depending on the photographic element being constructed, it is particularly desirable in one type of typical color photographic element containing a layer sensitized to each of the three primary regions of the visible spectrum, i.e., blue, green, and red, that a magenta trimmer dye absorb strongly at about 550 nm, and possess a sharp cutting bathochromic absorbance such that there is no appreciable absorbance above about 550 nm. Therefore it would be desirable to provide a filter dye for use in photographic elements that possesses high requisite absorbance in the green region of the spectrum below about 550 nm, but little or no absorbance above about 550 nm, and furthermore does not suffer from incubative or post process stain problems, and furthermore is not prone to migration in the coated film, but is fully removed upon processing.
One method used to incorporate solvent or water-soluble filter dyes into photographic film element layers is to add them as aqueous or alcoholic isotropic solutions. Dyes introduced by this method are generally highly mobile and rapidly diffusing and often wander into other layers of the element, usually with deleterious results. While the use of polymeric mordants can prevent dye wandering, such mordants aggravate the stain problem encountered when the dye remains in the element through processing.
Filter dyes have also been prepared as conventional dispersions in aqueous gelatin using standard colloid milling or homogenization methods or as loaded latices. More recently, ball-milling, sand-milling, media-milling and related methods of producing fine-particle-size slurries and suspensions of solid filter dyes have become standard tools for producing slurries and dispersions that can readily be used in photographic melt formulations. Solid particle filter dyes introduced as dispersions, when coated at sufficiently low pH, can eliminate problems associated with dye wandering. However, solvent-insoluble solid particle filter dyes (pigments) provide relatively low absorption coefficients, requiring that an excessive amount of dye be coated. In addition, it is very difficult to find classes of solid particle dispersion dyes which consistently yield useful, sharp-cutting bathochromic or hysochromic spectral features due to their microcrystalline nature. In fact the hue of a microcrystalline dye is highly unpredictable and often varies tremendously between similar analogs. In addition many solid particle dyes are not robust under keeping conditions of high heat and humidity experienced in melting and coating operations. Under such conditions, microcrystals of dye can undergo ripening, resulting in a lower optical density post incubation. In addition, the time and expense involved in preparing serviceable solid particle filter dye dispersions by milling techniques are a deterrent to their use, especially in large volume applications. It is therefore desirable to provide dye dispersions that do not necessarily require mechanical milling before use and that do not wander but that wash out easily during processing leaving little or no residual stain. It is also desirable that such filter dye dispersions provide high light absorption efficiencies with sharp-cutting absorbance peaks. One method of obtaining these desirable dye features in solid particle dispersions of oxonol filter dyes was described by Texter (U.S. Pat. No. 5,274,109, U.S. Pat. No. 5,326,687 and U.S. Pat. No. 5,624,467). Texter describes a process by which pyrazolone oxonol dyes are micro precipitated under strictly controlled pH conditions to produce absorbance spectra which are narrow, bathochromic and sharp cutting on the long wavelength side relative to their corresponding milled solid particle dispersions. This technique, however, is impractical for large volume applications.
A specific class of dyes, barbituric acid oxonol dyes, have been disclosed in commonly assigned copending U.S. application Ser. No. 08/565,480 filed Nov. 30, 1995, the entire disclosures of which are incorporated herein by reference, and U.S. Pat. No. 5,766,834 to possess sharp-cutting spectral properties when incorporated into gelatin coatings; however no reference is made to suggest that other filter dye classes might possess these useful spectral features. Further, the spectral features; of these dyes are limited to a few specific wavelength ranges, and the hue of these sharp-cutting dyes are not tunable over a large useful range.
It would be very useful if dye materials were available that were non-wandering, like solid particle dispersions, but were additionally narrowly absorbing and sharp-cutting in spectral features, like fully solvent-soluble dyes, and were additionally available at a wide variety of absorbance maxima useful in imaging elements.
Problem to be Solved by the Invention
It is therefore desirable to have a dye, especially a filter dye, which has a high extinction coefficient, a narrow halfbandwidth, and is sharp cutting on the bathochromic and/or hypsochromic edge, and even more preferably on both the hypsochromic and bathochromic edges. For dyes used in photographic elements, it is additionally desirable that the dye is capable of being substantially completely removed or rendered colorless on process of an exposed radiation-sensitive element comprising said dye. It is also desirable that the coated dye be robust in its spectral and physical properties and not prone to migration within the imaging element. It is also desirable to have a method for preparing a dispersion of a filter dye that is suitable for high-volume manufacture.